(1) Field of the Invention
The present invention relates generally to the synthesis of lower alkylene oxides and lower alkylene glycols and, more particularly, to a method and apparatus for the synthesis of lower alkylene oxides and lower alkylene glycols from lower alkanes and/or alkenes by selective partial oxidation.
(2) Description of the Prior Art
Ethylene oxide (EO) and ethylene glycol are currently manufactured from ethane and/or ethylene through a capital intensive, multi-step process. This conventional process utilizes a thermal cracker to make ethylene and other olefin hydrocarbons from ethane, propane, butane or naphtha hydrocarbons. The ethylene is separated from other byproducts, and is then epoxidized over a silver catalyst to produce ethylene oxide and other products including water and carbon dioxide. The ethylene oxide is then separated from these other reaction products and unconverted reactants. For further conversion to ethylene glycol (1,2-ethanediol or MEG), the ethylene oxide is mixed with a ten-fold or greater ratio of water and thermally hydrolyzed, though selective catalytic routes for EO to MEG are also currently being investigated.
Propylene glycol (1,2 propanediol or MPG) is similarly produced by hydrolysis of propylene oxide. The production of propylene oxide from propylene first requires production of a chlorohydrin intermediate by reacting propylene with chlorine and water. The chlorohydrin intermediate is then reacted with sodium hydroxide or calcium hydroxide to produce propylene oxide and sodium chloride or calcium chloride. A large volume of chloride salt byproducts is produced, and disposal of these salts is costly.
Other indirect routes are also known for producing propylene oxide. For example, isobutane can be reacted with oxygen to form t-butyl hydroperoxide, which in turn is reacted with propylene to produce propylene oxide and tert-butanol. The tert-butanol can then be reacted with methanol to produce the co-product methyl tertiary butyl ether (MTBE), a common gasoline additive. In another process, ethyl benzene is used as a starting material, and styrene is a resultant co-product. In each of these known processes for production of propylene oxide, a co-product results. Even though these co-products may sometimes be beneficial, they must always be handled and disposed of, and add accordingly to the cost of propylene oxide production.
Therefore, a process which could produce ethylene oxide, ethylene glycol, propylene oxide, propylene glycol, and other lower alkylene oxides and lower alkylene glycols directly from lower alkanes and/or lower alkenes as the starting hydrocarbon raw materials would provide a desirable advantage over the current prior art. For example, capital costs may be reduced by as much as fifty percent by eliminating the need for thermal crackers and associated equipment. A simpler manufacturing process would also reduce production costs and cycle times by eliminating intermediate steps in the conversion processes.
The present invention is accordingly directed to a method and apparatus for producing lower alkylene oxides and lower alkylene glycols by reacting at least one of a lower alkane and/or lower alkene with a source of oxygen and, optionally, a source of hydrogen to convert the lower alkane and/or lower alkene to at least one of the desired end products.
The necessary oxygen may be obtained from any suitable source, including without limitation, oxygen, ozone, and oxides of nitrogen. Preferably, oxygen is used to carry out the reaction. The O2 may be fed at any concentration by mixing with N2, He, or other inert gases. A convenient and safe source of oxygen is air. The required oxygen may also be provided by a suitable metal oxide catalyst or by the reaction of a metal oxide catalyst with N2O, NOx or sulfur oxides which may be generated in situ or supplied to the reaction system indirectly. The term metal oxide as used herein includes oxides of single metals or multiple metals. In a preferred embodiment of the invention, the oxygen is supplied by one or more reducible metal oxide catalysts that are regenerated by exposure to air, O2, other oxygen containing gases, or other suitable oxygen sources.
Additionally, a source of hydrogen may be directly or indirectly provided, for example, H2 gas. The necessary hydrogen may also be provided by one or more hydrogenation/dehydrogenation metal catalysts.
In the preferred embodiment, the invention includes a metal or mixed metal oxide catalyst, which provides a favorable standard free energy for the selective partial oxidation reactions. Metal oxide catalysts have been found to be particularly suitable for synthesizing ethylene oxide or ethylene glycol by epoxidation and dihydroxylation, respectively. These types of metal oxides (referred to herein as xe2x80x9cred-oxxe2x80x9d catalysts) allow for the ready accessibility of lattice oxygen to promote the oxidation of the feed materials, which results in a corresponding reduction of the metal oxide. This is followed by re-oxidation of the catalyst by another oxygen source, such as O2 or an oxygen-containing gas. Examples of effective red-ox catalysts include, but are not limited to, the oxides of cerium, iron, copper, nickel, lead, cadmium, molybdenum, vanadium, bismuth, manganese, barium, cobalt, strontium, tungsten, samarium, osmium, rhenium, rare earth elements, and mixtures of these oxides.
Those metals, which are generally known as hydrogenation/dehydrogenation metals, are also effective for carrying out the reaction, either alone or in combination with above-mentioned metal oxide catalysts. As explained in more detail below, it is believed that these catalysts generate highly reactive hydroperoxo and/or peroxo species from O2 and H2 and provide the oxygen and hydrogen necessary for the dihydroxylation or epoxidation reaction. These catalysts include but are not limited to nickel, palladium, platinum, cobalt, rhodium, iridium, iron, ruthenium, copper, zinc, gold, silver and mixtures of these metals.
Typically, both the red-ox and hydrogenation/dehydrogenation catalysts are supported on suitable carriers such as cerias, titanias, zirconias, silicas, aluminas, xe2x88x9d-alumina, silicon carbide, aluminum phosphate molecular sieves (AlPO""s), high silica molecular sieve zeolites, MCM-type large pore zeolites, mixtures of these carriers, and other catalyst support materials well-known in the art.
Thus, in the preferred embodiment, the apparatus includes a lower alkane/alkene supply; an oxygen supply for providing a source of oxygen; and a metal oxide catalytic reactor. The metal oxide catalytic reactor includes a reactor chamber; and a phosphate modified catalyst in the chamber for reacting the lower alkane/alkene supply with the source of oxygen to convert the lower alkane/alkene by selective partial oxidation to at least one of the ethylene oxide and ethylene glycol.
Both the red-ox and hydrogenation/dehydrogenation catalysts can be modified with a phosphorus containing salt. While not wishing to be bound by theory, it is believed that this phosphate modification provides for isolation of metal sites which makes the both the red-ox and hydrogenation/dehydrogenation catalysts more active and selective for the dihydroxylation or epoxidation of ethane to produce ethylene glycol and ethylene oxide, respectively. The phosphate-modified catalyst may be prepared by adding a phosphorus containing salt (e.g., phosphoric acid, ammonium dihydrogen phosphate, sodium phosphate, etc.) using techniques familiar to one skilled in the art. Alternatively, the phosphate may be incorporated during the forming of the re-dox or hydrogenation/dehydrogenation by coprecipitation, sol gel method, or other methods known to one skilled in the art.
Also, in the preferred embodiment, the apparatus further includes a separator for separating the ethylene oxide and the ethylene glycol from the total product stream and from unconverted reactants. The separator includes an input line, a distillation device, and a product output line. The distillation device may be a flash evaporator or a distillation column, wherein the evaporation or distillation is carried out under conditions known in the art to obtain the desired product purity.
The apparatus may include a recycle line for returning unconverted reactants back to the reactor. In addition, the product output line may include at least two product output streams when intermediate products are desired.
In the preferred embodiment, the lower alkane/alkene supply is selected from the group consisting of butane/butylene; propane/propylene; and ethane/ethylene. Also, preferably, the lower alkane/alkene supply is substantially sulfur-free and phosphorous-free to reduce possible poisoning of the catalyst. The lower alkane/alkene supply is a two-carbon hydrocarbon, which is preferably ethane and/or ethylene.
The oxygen supply for providing a source of oxygen is at least one of oxygen, ozone and oxides of nitrogen. Preferably, the source of oxygen is O2 or N2O. In the preferred embodiment, the source of oxygen is provided by at least one metal oxide catalyst. The metal oxide catalyst includes at least one metal oxide that is reduced by reaction with a hydrocarbon moiety to a lower oxidation state such that the metal oxide provides a lower standard free energy for the selective partial oxidation of the lower alkane/alkene. The metal oxide may be selected from the group consisting of oxides of cerium, iron, copper, nickel, lead, cadmium, molybdenum, vanadium, bismuth, manganese, barium, cobalt, strontium, tungsten, samarium, osmium, rhenium, rare earth elements, and mixtures of these oxides. The metal oxide may be selected from the group consisting of NiO, PbO, CdO, MoO3, V2O4, V2O5, BiO, Bi2O3, CuO, Cu2O, MnO2, Mn2O3, Mn3O4 BaO2, Co3O4, SrO2, WO2, WO3, SnO2, CeO2, OsO4, Re2O7, FeO, Fe2O3, Fe3O4, rare earth oxides, and mixtures thereof.
The resulting alkylene oxides and alkylene glycols are substantially free of higher hydrocarbons greater than four carbon numbers.
According to the present invention, the metal oxide catalyst is regenerable. In the preferred embodiment, the metal oxide catalyst is regenerated by exposing the metal oxide catalyst to a source of oxygen, such as in a fixed bed, fluid bed, circulating fluidized bed, or other suitable reactor. Also, in the preferred embodiment, the apparatus may further include a hydrogen supply for providing a source of hydrogen in addition to the oxygen supply for providing a source of oxygen.
In the preferred embodiment, the phosphate-modified catalyst is iron phosphate. However, hydrogenation catalyst may work as well. The catalyst may further include a catalytic modifier, such as a platinum-containing compound, which improves the activity and/or selectivity of the catalyst. Other modifiers may also be used such as alkali and alkaline earth oxides. The apparatus may also include a carrier for supporting the phosphate-modified catalyst. In the preferred embodiment, the carrier is selected from the group consisting of: cerias, titanias, zirconias, silicas, aluminas, xe2x88x9d-alumina, silicon carbide, aluminum phosphate molecular sieves (AlPO""s), high silica molecular sieve zeolites, MCM-type large pore zeolites, mixtures thereof.
The present invention is operable to react the ethane/ethylene with oxygen to form the at least one of ethylene oxide and ethylene glycol and preferably forms ethylene glycol. However, the ethane/ethylene may also form higher glycols selected from the group consisting of diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (T4G).
As is expected the higher glycols are also formed as a result of condensation of the formed glycols and/or ethoxylation. In general, the lower glycol is preferred, but higher glycols may be formed preferentially by running at higher alkane/alkene conversions, or by recycle of the alkylene glycols back to the reactor.
Accordingly, one aspect of the present invention is to provide a method and apparatus for synthesizing at least one of alkylene oxides and alkylene glycols from lower alkanes and/or lower alkenes, the apparatus including: a lower alkane/alkene supply; an oxygen supply for providing a source of oxygen; and a metal oxide catalytic reactor for reacting the lower alkane/alkene supply with the source of oxygen to convert the lower alkane/alkene by selective partial oxidation to at least one of the alkylene oxides and alkylene glycols.
Another aspect of the present invention is to provide a metal oxide catalytic reactor for an apparatus for synthesizing at least one of alkylene oxides and alkylene glycols from lower alkanes and/or lower alkenes, the metal oxide catalytic reactor including: a reactor chamber; and a phosphate modified catalyst in the chamber for reacting the lower alkane/alkene supply with the source of oxygen to convert the lower alkane/alkene by selective partial oxidation to at least one of the alkylene oxides and alkylene glycols.
Still another aspect of the present invention is to provide a method and apparatus for synthesizing at least one of alkylene oxides and alkylene glycols from lower alkanes and/or lower alkenes, the apparatus including: a lower alkane/alkene supply; an oxygen supply for providing a source of oxygen; a metal oxide catalytic reactor, the metal oxide catalytic reactor including: a reactor chamber; and a phosphate modified catalyst in the chamber for reacting the lower alkane/alkene supply with the source of oxygen to convert the lower alkane/alkene by selective partial oxidation to at least one of the alkylene oxides and alkylene glycols; and a separator for separating the alkylene oxides and alkylene glycols from the total product stream and unconverted reactants.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.